Waste Treatment Septic Systems

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Waste Treatment Septic Systems

• Lab 7

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Objectives

• Know how a conventional septic system works.
• Be able to describe three alternative systems
  that could be used to dispose of household waste.
• Know what soil conditions are needed for proper
  functioning of conventional and alternative waste
  disposal systems.

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Background Info

• Every day the average U.S. family of four
  generates approximately 200 gallons of sewage
  effluent through use of toilets, showers,
  bathtubs, sinks, washing machines, and
  dishwashers.
• This sewage is 95 water and 5 solid material.

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Disposing of the Material

• In houses connected to city sewer systems,
  disposal of household sewage is simple the waste
  water simply flows out of the houses, and down
  into the city sewer pipe.
• However, in N. C., about 50 of the houses
  (approximately 1.5 million) are not connected to
  city a sewer, and wastes from these homes must be
  disposed of in other ways, usually on the
  homeowner's property.

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Septic Systems

• The easiest way to dispose of most household's
  daily sewage is to let it seep into the soil
  surrounding the home.
• To do this, most of the solid materials are first
  removed from the effluent, and then the
  wastewater is spread over the soil and allowed to
  seep in.

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Soils Role in the Process

• The soil's job is to filter out any remaining
  solids, and to kill the germs in the effluent.
• The purified water flows downward through the
  soil to the water table and should be fit to
  drink once it reaches the water table.

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Schematic of Septic System
http//www.cet.nau.edu/Projects/WDP/resources/Conv
entional_Overview/ConventionalSepticSystem.jpg
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Septic Tank
http//www.co.thurston.wa.us/health/ehoss/images/d
rainfield.jpg
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Septic Tank

• The septic tank is a settling tank where sewage
  from the house is stored temporarily so that
  solid materials settle to the bottom of the tank
  to form sludge, while grease floats to the top to
  form a scum layer.
• The scum and sludge must be periodically removed
  from the septic tank by simply pumping them out.

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Septic Tank
http//rps.uvi.edu/CES/septicx.jpg
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Drainfield or Absorption Field
http//www.co.thurston.wa.us/health/ehoss/images/d
rainfield.jpg
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Drainfield

• The absorption field is frequently a network of
  drain lines (pipes with holes in them) that carry
  wastewater from the septic tank and apply it to
  the soil.
• The size of the absorption field varies from site
  to site, but most are small enough to fit in a
  backyard and cover and area between 400 and 800
  ft2.

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Suitable Soils

• Although effluent can be applied to the surface
  of any soil, not all soils are able to absorb and
  purify wastewater.
• Soils that can be used for waste disposal are
  permeable, deep, well drained (not waterlogged)
  and are not on a steep slope.
• In N. C., state law requires that all soils pass
  an inspection before a septic system is installed
  on any property.

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Alternative Septic Systems

• If a soil is not suitable for a conventional
  septic system, several alternative systems have
  been developed to overcome specific soil
  problems.
• These alternative systems include the low
  pressure pipe system, the mound system, and the
  recirculating sand filter.

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Low Pressure Pipe System

• The Low Pressure Pipe system (LPP) includes a
  small pump, which may turn on 1-2 times a day, to
  pump a large amount of effluent to the
  drainfield.
• This allows the soil to absorb and filter the
  effluent effectively.

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Mound System

• Soils with shallow depth over a limiting layer or
  soils with high percolation rates may be suitable
  for a mound system.
• In a mound system,specially selected sand is
  placed on top of the natural soil to help treat
  and dispose of septic tank effluent.

http//ohioline.osu.edu/aex-fact/images/744_1.jpg
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Recirculating Sand Filter
Effluent In
http//www.nesc.wvu.edu/nsfc/pdf/eti/RSF_tech.pdf
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How do we determine if our soils are suitable?

• The ability of a soil to properly absorb and
  treat sewage waste will depend on several soil
  properties.
• Each County Health Department should be consulted
  for specific criteria used in a given county.
• Remember that these are the rules that state
  whether or not you can build a soil drainfield on
  your land.

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General Order of Events

• Determine the types of soils on the lot.
• Find out what type of septic system, if any, will
  work on those soils.
• Obtain a septic system improvement permit (IP)
  from your local health department.
• Obtain a cost estimate for installing the kind of
  septic system you need. Ask about the operating
  requirements and maintenance costs for the
  system.

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Reviewing the Site

• Walk over each lot and look for indications of
  soil problems or site limitations that could
  affect the performance of a septic system.
• Look for steep slopes, streams nearby, wet soils,
  wetlands, bedrock protruding, etc.

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Reviewing the Soils

• If you do not observe any obvious site problems,
  you may wish to identify the soil types.
• The county soil survey report shows which soils
  are most likely to occur on the land you are
  investigating.
• You can use this report to help screen land
  parcels and focus your efforts upon those lots
  that have the most desirable soil and site
  characteristics.
• Do not substitute it for an on-site evaluation of
  soil and site conditions.

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Unsuitable Soils

• Unfortunately, not all soils can absorb
  wastewater or purify it.
• Septic systems that are installed in unsuitable
  soils usually malfunction by leaking raw,
  untreated sewage to the soil surface or a
  roadside ditch, or by contaminating the
  groundwater.
• The sewage may contain deadly bacteria and
  viruses.

http//www.ncdc.gov.uk/media/images/d/l/WaterPollu
tion_640.JPG
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Are the soils suitable?

• In order to determine if a soil is suitable, a
  basic morphological description including
  texture, structure, color and clay type is
  required.
• We must first complete a description of the soils
  and then follow the guidelines provided by NC.

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Soil Suitability in NC Landscape Position

• gt30 Slope, Floodplain or Depressional Area
  Unsuitable (US)
• 15-30 Slope Provisionally Suitable (PS)
• lt15 Slope Suitable (S)

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Soil Suitability in NC Textural Class

• Group I Sand Loamy Sand S
• Group II Sandy Loam Loam S
• Group III Sandy Clay Loam, Silt Loam, Silty
  Clay Loam Clay Loam PS
• Group IVa 11 Clay (Kaolinite) PS
• Group Ivb 21 Clay (Montmorillonite or
  Vermiculite) US

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Soil Suitability in NC Structure

• All Groups are S, except
• Groups III IV with blocky structure PS
• Groups III IV with platy structure US
• Groups II. III IV with massive structure US

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Soil Suitability in NC Organic Soils

• All organic soils are unsuitable (US).

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Soil Suitability in NC Drainage

• To determine the suitability, we need to look for
  depth to seasonal high water table (chroma lt2
  indicates reducing conditions).
• gt 4 ft S
• 3-4 ft PS
• lt3 ft US

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Soil Suitability in NC Restrictive Horizons

• To determine suitability, we must locate any
  restrictive layers (clay pans, etc.) or the C
  horizons. If we have either of these, use the
  following
• gt 4 ft S
• 3-4 ft PS
• lt3 ft US

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Determining Loading Rates

• Now we must determine how much effluent we can
  load onto the drainfield so that the system works
  properly.

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Loading Rates
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How big must the drainfield be?

• The loading rates and the size of the house are
  used to determining how large the soil drain
  field must be.
• The rule of thumb is 120 gpd of effluent for each
  bedroom in the house.
• For example a 3-bedroom house is expected to
  produce 3 X 120 gpd effluent or 360 gpd of
  effluent.

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Requirements for a Conventional System

• lt30 Slope
• gt3 ft to seasonal high water table, bedrock,
  saprolite or restrictive horizon
• Suitable (S) or Provisionally Suitable (PS)
  texture and structure to 3 ft.

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Requirements for Low Pressure Pipe Systems

• Soil depth gt 2 ft to seasonal high water table,
  bedrock, saprolite or restrictive horizon
• S or PS texture and structure to 3 ft.

http//www.ces.ncsu.edu/plymouth/septic2/FAST-Comp
lete1.gif
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Requirements for Mound Systems

• lt 10 Slope
• Soil depth gt1 ft to seasonal high water table,
  bedrock, saprolite or restrictive horizon
• S or PS texture and structure to 1 ft.

http//www.co.kenosha.wi.us/plandev/images/mound01
.jpg
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Our Turn

• For this lab, we will review soil profiles and
  determine whether or not the soil would be
  suitable for a conventional septic system.
• If it is not, we will determine if an alternative
  system could be used.
• Please see the Lab 7 Help file for any help on
  the lab.

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Questions?